The invention is directed to a method for turning off a starter of an internal combustion engine.
It is known that internal combustion engines must be started by means of a starting mechanism because they cannot start by themselves. Starter motors are usually used for this purpose. These starter motors are connected with a voltage and source via a starter relay constructed as an engagement relay, as they are called, and a pinion of the starter motor is simultaneously engaged with a toothed rim of a flywheel of the internal combustion engine for cranking. In order to switch on the starter relay, it is known to control this starter relay by means of an external switch, for example, an ignition switch or starter switch of the motor vehicle. After the internal combustion engine has begun to run independently, the starter motor must be disengaged to prevent noise and wear. It is known to switch off the starter manually by releasing the ignition switch or starter switch. Solutions for turning off the starter of the internal combustion engine automatically for increased convenience in motor vehicles are known. For example, it is suggested in DE 195 03 537 A1 to detect autonomous running of the internal combustion engine automatically by detecting the ripple of a battery voltage or a starter current. The absolute value of the battery voltage or starter current is compared with a reference value in order to detect independent running of the internal combustion engine. In this connection, it is disadvantageous that operating conditions of the internal combustion engine can be taken into account only insufficiently, so that a cold start and warm start of the internal combustion engine, for example, cannot be taken into account.
The method according to the invention offers the advantage that information about the operating state of the internal combustion engine can be taken into account indirectly for determining the time to switch off the starter. Due to the fact that a signal proportional to the starter current is evaluated for determining the time to switch off the starter, wherein there is an evaluation of a characteristic line with a signal which is proportional to the starter current, which characteristic line is dependent on the operating state of the internal combustion engine, it is possible to switch off the starter in an optimum manner immediately after the internal combustion engine has begun to run independently, so that starting time is reduced especially when the internal combustion engine is at operating temperature. The method can be used in a simple manner for all internal combustion engines, wherein it is only necessary to adapt that characteristic lines of the parameters determined by the operating state of the internal combustion engine.
In a preferred construction of the invention, a battery voltage of a motor vehicle battery supplying the starter motor is evaluated as a signal proportional to the starter current. In this way, it is possible to optimize the time for switching off the starter without information about the rate of rotation of a crankshaft of the internal combustion engine.